1. Field of the Invention
The present invention relates to a cooling device that cools down a sheet-like member used in an image forming device such as a printer, a facsimile, and a copy machine, and an image forming device.
2. Description of the Related Art
Image forming devices that form a toner image on a paper that is a sheet-like member using an electrophotography technique and gets the toner image through a heat fixing device to melt and fuse a toner have been known. Generally, the temperature of the heat fixing device depends on a type of a toner or a paper or a paper transport speed but is controlled to be set to a temperature of about 180° C. to 200° C. to quickly fuse the toner. A surface temperature of the paper after passing through the heat fixing device depends on a heat capacity (e.g., specific heat or density) of the paper but has a high temperature of, for example, about 100° C. to 130° C. Since a melting temperature of the toner is lower, at a point in time directly after passing through the heat fixing device, the toner is in a slightly softened state and is in an adhesive state for a while until the paper is cooled down. Thus, when an image output operation is continuously repeated and papers having passed through the heat fixing device are stacked on a discharge paper receiving unit, if the toner on the paper is not sufficiently hardened but in a soft state, the toner on the paper may be attached to another paper, so that a so-called blocking phenomenon may be caused, remarkably degrading the image quality.
In an image forming device disclosed in Japanese Patent Application Laid-Open (JP-A) No. 2006-003819, a cooling device with a cooling roller that is rotatably supported to a bracket through a bearing and comes in contact with a paper to cool down the paper while transporting the paper is disposed at a down stream side of a heat fixing device in a paper transport direction. The paper having passed through the heat fixing device is cooled down by the cooling roller of the cooling device, so that the toner on the paper is also cooled down and hardened, thereby preventing the occurrence of the blocking phenomenon. The cooling roller has a tubular structure. A cooling liquid flows inside the cooling roller from one end side to the other end side in a longitudinal direction of the cooling roller, and so the cooling roller raised in temperature by depriving heat from the paper is cooled down by the cooling liquid.
In a configuration in which the cooling liquid flows inside the cooling roller from one end side to the other end side in the longitudinal direction of the cooling roller, a rotary joint connecting a pump for feeding the cooling liquid with the cooling roller through a tube needs to be disposed at both ends of the cooling roller, which may lead to a large-sized image forming device. For this reason, as illustrated in FIG. 54, a cooling device in which a rotary joint 135 is disposed at one side of the cooling roller 122 is used. Therefore, compared to the case where the rotary joint 135 is disposed at both ends of the cooling roller 122, the size of the image forming device can be prevented from being increased.
The cooling roller has a dual tube structure in which an inner tube is disposed inside an outer tube, and an outside flow passage that allows the cooling liquid to flow through a space between the outer tube and the inner tube and an inside flow passage that allows the cooling liquids to flow inside the inner tube are formed. The cooling liquid flows in the outside flow passage and the inside flow passage from one end side to the other end side in the axial direction of the cooling roller and deprives the paper of heat, so that the cooling roller having a high temperature is cooled down by the cooling liquid. Since the cooling roller has the dual tube structure, the cooling liquid flowing through the outer flow passage can be cooled down as the cooling liquid flowing through the inner flow passage receives heat of the cooling liquid, heated by heat from the cooling roller, flowing through the outer flow passage, whereby the cooling performance of the cooling roller can be increased. In the configuration in which the cooling liquid flows through the outside flow passage and the inside flow passage inside the cooling roller from one end side to the other end side in the longitudinal direction of the cooling roller, a rotary joint connecting a pump for feeding the cooling liquid with the cooling roller through a tube is mounted to both ends of the cooling roller.
The cooling roller 122 illustrated in FIG. 54 has a dual tube structure in which an inner tube 122b is disposed inside an outer tube 122a, and an outside flow passage that allows the cooling liquid to flow through a space between the outer tube 122a and the inner tube 122b and an inside flow passage that allows the cooling liquid to flow inside the inner tube 122b are formed. The cooling roller 122 is rotatably supported to a bracket 134 of the cooling device through bearings 140 and 141. An opening 122m is formed in an end section of the inner tube 122b at the rotary joint 135 side, and an opening 122k allowing the outside flow passage to communicate with the inside flow passage is formed in an end section of the inner tube 122b at a side opposite to the rotary joint 135 side. The cooling liquid is fed to the inside of the rotary joint 135 through a feed port formed in the rotary joint 135, passes through the outside flow passage, and flows into the inside of the inner tube 122b through the opening 122k. The cooling liquid flowing into the inside of the inner tube 122b passes through the inner tube 122b, is drained to the outside of the inner tube 122b through the opening 122m, and is drained from a drain port formed in the rotary joint 135.
In the cooling roller 122 illustrated in FIG. 54, the inner tube 122b is supported to the rotary joint 135 in a cantilever state. For this reason, a free end of the inner tube 122b easily vibrates by the flow of the cooling liquid fed to the inside of the outer tube 122a. The vibration is transmitted from the inner tube 122b to the rotary joint 135, so that the rotary joint 135 vibrates. Further, since the outer tube 122a and the rotary joint 135 are screw-coupled by screws thereof and fixed, rattling is harsh, so that axis misalignment between the outer tube 122a and the rotary joint 135 is likely to occur. If axis misalignment between the outer tube 122a and the rotary joint 135 occurs, the rotary joint 135 vibrates due to eccentricity when the outer tube 122a rotates.
If the rotary joint 135 vibrates, a load is applied to a coupling section between the outer tube 122a and the rotary joint 135, and thus there occurs a problem in that durability is lowered, and the cooling liquid leaks from the coupling section. Further, the vibration of the rotary joint 135 is transmitted to the outer tube 122a, and rotation accuracy of the outer tube 122a is lowered. Therefore, there occurs a problem in that the sheet-like member is not properly transported.
The inventors of the present application conducted an experiment in a state in which the cooling device in which the rotary joint is mounted to both ends of the cooling roller is mounted in the image forming device that performs image forming at a high speed. At this time, a phenomenon that the rotary joint vibrates occurred. If the rotary joint vibrates, a load is applied to the coupling section between the outer tube and the rotary joint, and thus there occurs a problem in that durability is lowered, and the cooling liquid leaks from the coupling section. Further, the vibration of the rotary joint is transmitted to the outer tube, and the rotation accuracy of the outer tube is lowered. Therefore, there occurs a problem in that the sheet-like member is not properly transported.
As a result of repetitively doing research with all their heart, the inventors of the present application found out that the rotary joint vibrates due to the following reasons. If the outer tube and the rotary joint are screw-coupled by screws thereof and fixed, rattling is harsh, so that axis misalignment between the outer tube and the rotary joint is likely to occur. Further, if the inner tube and the rotary joint are screw-coupled by screws thereof and fixed, rattling is harsh, so that axis misalignment between the inner tube and the rotary joint is likely to occur. If axis misalignment occurs between the inner tube and the rotary joint, axis misalignment occurs between the rotary joint mounted to the one end side of the inner tube and the rotary joint mounted to the other end side. Then, axis misalignment also occurs between the outer tube and the rotary joints. Accordingly, it was found out that axis misalignment occurred between the outer tube and the rotary joints causes eccentricity when the outer tube rotates, vibrating the rotary joint.
Meantime, as an image forming process speed of the image forming device of the electrophotography type increases, the image forming device of the electrophotography type started to be used for the purpose of continuously performing an image forming process (a printing process) over a long time (for example, several days) by continuously passing a recoding medium such as a paper, as in a printing process. The image forming device of the electrophotography type can perform an image forming process of 100 to 120 pieces of A4-size papers per minute and thus is called as a high speed machine. If the cooling roller rotates to satisfy high speed printing of 100 to 120 pieces per minute, the above-described problem resulting from vibration of the rotary joint becomes remarkable. That is, as the cooling roller rotates at a high speed, a burden of the coupling section between the outer tube and the rotary joint increases, so that there is a possibility that the cooling liquid will leak or the vibration of the rotary joint will influence image forming.